Ferrimagnetic garnet compositions



Dec. 13, 1966 G. P. ESPINOSA ETAL 3,291,749

FERRIMAGNETIC GARNET COMPOSITIONS Filed NQV. 29, 1963 2 Sheets$heet l 2FIG.

TEMPERATURE IN DEGREES KELl/IN G. R ESP/NOSA INVENTORS 5. GEL L ER 0 14L By 0.5 1.0 L5 x 4&2

ATTORNEY 13, 1965 G. P. ESPINOSA ETAL. 3,291,740

FERRIMAGNETIC GARNET COMPOSITIONS Filed Nov. 29, 1963 2 Sheets-Sheet 2FIG. 3

I i I 0 I00 200 300 TEMPERATURE /N DEGREES AELV/N Fl 6. 4 F/ G. 5

O 0.5 1.0 35 1 A X 0.5 lo I 5 United States Patent G 3,291,740FERRIMAGNETIC GARNET COMPOSITIONS Gerald P. Espinosa, Summit, andSeymour Geller, Morristown, N.J., assignors to Bell TelephoneLaboratories, Incorporated, New York, N.Y., a corporation of New YorkFiled Nov. 29, 1963, Ser. No. 326,675 7 Claims. (Cl. 252-625) Thisinvention relates to synthetic garnets and their preparation.

The discovery of synthetic garnets, and in particular yttrium irongarnet, has provoked new interest in the field of ferrimagneticmaterials and has resulted in more useful and effective devices,particularly those employed for microwave communications. The garnetmaterials, aside from possessing exceptional ferrimagnetic properties,do not tolerate distortions in symmetry and generally form onlyaccording to precise stoichiometry. This property permits a degree ofreproducibility in the synthesis of these materials which is notablylacking in the synthesis of spinel ferrites.

Since this discovery there have 'been several attempts towardsubstitutional modifications of yttrium iron garnet in an effort todiscover enhanced or new characteristics. As a result the art hasdeveloped, characteristically by systematic and empirical methods, acatalogue of various elements which will substitute into the garnetstructure. Certain of the substituted garnets have useful and unexpectedproperties such as those described and claimed in United States Patents3,006,854 and 3,006,855, both issued October 31, 1961, and United StatesPatent 3,156,- 651, issued November 10, 1964, and applications SerialNos. 293,962 and 293,963, both filed July 10, 1963.

In the garnet compositions there is a strong interaction between theoctahedrally and tetrahedrally situated iron ions. It is found that themagnetic. moments of magnetic ions occupying these sites oppose oneanother. Thus the over-all moment of a ferrimagnetic garnet such asyttrium iron garnet is attributed to the numerical prevalence of thethree tetrahedrally located ferric ions over the two octahedral ions.Thus it 'becomes evident that a nonmagnetic substitution in thetetrahedral site initially reduces the moment of the garnet whereasoctahedral substitutions initially increase the magnetic moment of thegarnet. A garnet system illustrating this principle is described andclaimed in the aforementioned application Serial No. 183,201.

This invention is'directed to a novel garent system in which antimony issubstituted for ion in the octahedral sites. Other aspects of theinvention involve companion substitutions each of which results in agarnet material having useful and desirable ferrimagnetic properties. Amore specific embodiment of the invention is a ferrimagnetic garnetcomposition containing antimony which is devoid of any rare earth ions.Rare earth elements are difiicult and expensive to obtain in pure form.Hence garnets which include rare earth elements generally containimpurities which broaden the ferromagnetic resonance line Width. Theelimination of rare earth ions from the garnet not only results inenhanced ferrimagnetic properties but also effects a cost saving.

The ferrimagnetic garnet compositions within the scope of this inventionare represented 'by the formula:

where Me is yttrium or bismuth, X is a divalent compensating ion such ascalcium, and A, B and C are related and limited according to thefollowing relationships:

tion for the compositions:

These and other aspects of the invention may be more easily understoodwhen considered in the following detailed description. In the drawing:

FIG. 1 is a plot of spontaneous magnetization n vs. temperature for thecomposition:

FIG. 2 is a plot of spontaneous magnetization n vs. composition forcompounds represented by the general formula:

32x 2x x 2x] e 12 FIG. 3 is a plot of spontaneous magnetization n vs.temperature for various compositions of the formula:

3-2x 2x x 2-x] e 12 FIG. 4 is a plot of spontaneous magnetization n vs.composition for various materials of the formula:

d {Caz} x 2xl 1.5+x 1.5x) 12 an FIG. 5 is a plot of the latticeconstant, a, vs. composi i sll x mxl l.5+x 1.5-x) 12 aul X Z-X] 3) 12Referring to FIG. 1 there is shown the variation of spontaneousmagnetization n in Bohr magnetons per formula weight with temperature indegrees Kelvin. Curve 10 is for the composition FIG. 2 is a plot ofmagnetization n again in Bohr- Magnet ons per formula unit vs.composition with curve v 20 describing the moment for compositions ofthe general formula:

{ 32X zX x 2-x] B) 012' where x is varied as the abscissa.

occurs at a value of x=0.6.

:1 FIG. 3. is aplot of spontaneous magnetization n vs. temperaturesimilar. to that of..FIG. l for three compositionshaving the generalformula:

s 2x 2x x 2x] e) 12 Curves 30, 31 and 32 show this relationship for theThe peak moment compositions in which x equals 0.5, 0.6 and 0.7,respectively.

FIG. 4 is a plot of spontaneous magnetization n vs. composition for thegarnet having the general formula:

The lattice constants are useful in converting the spontaneousmagnetization n which is based on formula units to a weight or volumemagnetization unit. One such calculation can he made according to theformula: I

whene 41'rM is the familiar measureof magnetization per unit volume ofgarnet, n isthe magnetization per formula unit, 5585 is the equivalentto the number of gauss/ Bohr magneton, MW is the molecular weight and pis the density. The lattice constant a is necessary for the calculationof the density according to the relationship:

where p is the density, 1. 66 is the reciprocal of Ayaxgadros numbermultipled by 10 8 is thenumber of formula units in the crystallographicunit cell, MW is the molecular weight, andV is the volume per formulaunit in Augstroms Values oi 41rM for exemplary compositions of theinvention are given in the following table. The column 2: prescribes thecomposition from the formula:

TABLE I z u 41rM (at K.)

gauss/oc.

The samples used for these measurements were prepared according to thefollowing examples.

Example I The composition 2 0.s 1.s] a) 12 was prepared 'from thefollowing starting materials:

Grams Y O 0.2258. CaCO 0.1001 Sb203 0.0729 F6203 0.3593

These materials were ground together in an agate mortar after which theywere compacted in a steel die. The ground material was formed into apellet which was calcined over a temperature range of 500 C. to 950 C.following a schedule such that the maximum temperature was attained in aperiod of about one hour.

The calcined pellet was then fired according to the schedule:

Hours 1050 C /2 I350 C. 23

Between the designated ifirin-g steps the mixture was reground. Theregrindiug procedure was used in every example described.

The resulting product in this and all the following examples was asingle-phase gar-net as determined by X-ray diffraction analysis. a

. Example II The composition 1.8 1.2 0.6 1.] z Q12" was prepared fromthe following. starting materials:

. Grams. Y O .J 0.2032 CaCo 0.120 1 $13203 Fz03 Q These materials wereground and calcined as in Example I. The calcined material was firedaccording to the conditions:

. Hours Example 111 The composition was prepared by mixing together thefollowing ingreclients:

. Grams Y O 0.1807 CaCO 0.1401 Sb O 0.1020

The mixture was ground, calcined as in Examples I and II, andfired-under the following conditions:

. Hours 1100 C. /2 1310 C. 16

Example IV The composition {Y F6] (F3)O12 was prepared from thematerials:

Grams Y203 Ca O 0.2002 Sb O 0.1458 Fe O 0.3194

The mixture was ground, calcined as before, and fired according to theschedule:

The mixture was ground and calcined as in the previous examples andfired according to the schedule:

Hours 1075 C. to 1050 C. 2 /2 1125 C. 2 1130 C. 11

Example VI The garnet composition a o.s 1.'zl 1.B 1.2) 12 was preparedby mixing together the following ingredients:

I Grams CaCO "0.3003 Sb O I 0.0437 F3203 V 0 0.1091

The mixture was ground and calcined as before and fired according to theschedule:

7 Hours ':1100 C. /2 1160 C M 16 1175" C. 67

'5 Example VII The garnet composition- {Caz} l ds rsl ao 12 was preparedby combining the following ingredients:

Grams CaCO 0.3003 $15 0 0.0729 F5203 V 0 0.0910

The mixture was ground and calcined as in the previous examples andfired according tothe schedule:

Hours 1100 C /2 1215 C. 42 1200 C. 22

Example VIII The garnet composition {Caz} o.'15 1.25] aae oasl 12 wasprepared by mixing together the following materials:

Grams CaCO 0.3003 Sb O 0.1093 Fe O 0.2795 V 0 0.0682

The mixture was ground and calcined as previously prescribed and firedaccording to the schedule:

Hours Example IX The garnet composition was prepared by mixing togetherthe following materials:

' Grams Y O 0.0790 CaCO 0.2302 Sb O 0.0838 Fe O 0.3074 V 0 0.0523

The mixture was ground and calcined as inExample I and fired accordingto the schedule:

Hours 1200 C. 22 1255 C. 64 1300 C. 17

Example X The garnet composition o.'1 2.a} 0.575 1.425] mzs as'lsl 12was prepared by combining the following materials:

Grams Bi O 0.1631 CaCO 0.2302 $11 0 0.0838 F6203 V 0 0.0523

-The mixture was ground and calcined as prescribed earlier and firedaccording to the schedule:

Example XI The garnet composition I as m o.s5 1.45l 2.45 o.55) 12 wasprepared by combining the -following ingredients:

Grams Bi o 0.1864 CaCO 0.2202 Sb O 0.0802 Fe O 0.3195 V 0 0.0500

The mixture was ground and calcined as in Example I and fired accordingto the schedule:

Hours 1000 C. /2 1035 C. c 2 1020 C. l5 1060 C. 18 975 C. 48

Various data obtained from these and other samples is given in thefigures described previously.

Each of the examples provides for the preparation of a 0.001 molequantity of the composition indicated. While each example is directed tothe preparation of a single-phase garnet, it is well known that certaincommercial applications do not require a material of such perfection. Infact, many commercial ferrimagnetic materials show the presence of morethan one second phase. Accordingly, it is not intended that theinvention be limited to the preparation of a single-phase materialexcept insofar as some garnet phase is present. Under certaincircumstances, such second-phase may be desirable for the purpose, forexample, of diluting the magnetic properties in the material and,accordingly, may be deliberately added. In general, there are nomaterials which are necessarily to be avoided, either as con taminantsor intentionally included ingredients. In fact, certain ingredientsserving purposes already recognized in related YIG and substituted YIGsystems may be included. Such ingredients include, for example,aluminum, gallium, scandium, tin, germanium, silicon, et cetera. Reducedmoment is a desideratum in certain low frequency devices operating onthe parametric principle. It is to be noted, too, that calcium, whilepreferred from the standpoint of atomic size, is merely a compensatingion permitting the introduction of vanadium into the structure. Anycompensating ion in size and amount which :may be accepted by thestructure may be substituted.

Single crystals of the garnets described herein may be prepared byvarious known crystal growth techniques. For certain applications it isdesirable to use singlecrystal material which is also obviously withinthe scope of the invention.

Various other modifications and extensions of this invention will becomeapparent to those skilled in the art. All such variations and deviationswhich basically rely on the teachings through which this invention hasadvanced the art are properly considered within the spirit and scope ofthis invention.

What is claimed is:

1. A synthetic garnet composition having the formula:

7 8 where 'Me is selected from the group consisting of yttrium where Meis selected from the group consisting of yttrium and bismuth, and A, Band C are related and limited and bismuth, and A, B and C are relatedand limited acaccording to: cording to:

a I B+C= /2A B+C= /2A A=0.1 to 3 5 A=0.3 to 3 B=0.05 to 1.5 and I vB=0.l to 1.5 and C=zero to 1.5 v C-'-zero to 1.5 2. The composition ofclaim 1 wherein A equals 3, which comprises mixing together thestoichiornetric pro- 4 3. The"dmpositi0n of claim' l'wherein Me'isbismuth, portions of each cation and firing the mixture at a tem- 4. Thecomposition of-claim 1 wherein B has a value 10 Pefflture the nge 50 C.to 1350" C. of 0.5.

5. The compositionvof claim 1 wherein B has a value References Cited bythe'Examinel' of 0.6. UNITED STATES PATENTS 6. The composition of-claim1 wherein B has a value 15 2 337 433 1953 Hakka!- et 252 2 of 0.7.3,003,966 10/1961 Van Uitert 252-625 7. A method for preparing a garnetmaterial having the formula: TOBIAS E. LEVOW, Primary Examiner;

1. A SYNTHETIC GARNET COMPOSITION HAVING THE FORMULA: